A catalytic hydrocarbon fuel reformer converts a fuel stream, comprising, for example, natural gas, light distillates, methanol, propane, naphtha, kerosene, and/or combinations thereof, and water vapor into a hydrogen-rich reformats stream. The hydrogen-rich reformats stream is generally suitable for use as the fuel gas stream to the anode of an electrochemical fuel cell after passing through a water gas shift reactor and other purification means such as a carbon monoxide selective oxidizer. In the conversion process, the raw hydrocarbon fuel stream is typically percolated through a catalyst bed or beds contained within reactor tubes mounted in the reformer vessel. The catalytic conversion process is normally carried out at elevated catalyst temperatures in the range of about 1200.degree. F. to about 1600.degree. F. Such elevated temperatures are generated by the heat of combustion from a burner incorporated in the reformer.
The search for alternative power sources has focused attention on the use of electrochemical fuel cells to generate electrical power. Unlike conventional fossil fuel power sources, fuel cells are capable of generating electrical power from a fuel stream and an oxidant stream without producing substantial amounts of undesirable byproducts, such as sulfides, nitrogen oxide and carbon monoxide. However, the commercial viability of utility-based fuel cell systems depends in part on the ability to efficiently and cleanly convert conventional hydrocarbon fuels sources, such as natural gas (methane), to a hydrogen-rich reformate gas stream. Properly designed catalytic hydrocarbon reformers can generate the required reformate gas streams with increased reliability and decreased cost.
With respect to reliability and cost, conventional industrial catalytic hydrocarbon reformers have at least two major disadvantages with respect to fuel cell use. First, because conventional reformers operate at very high temperatures and pressure differentials, the reformer tubes which contain the catalyst must be constructed of rugged, thick walled portions of expensive materials capable of withstanding high temperature operating conditions. Additionally, conventional reformers also tend to be quite large, which again impacts material costs and the cost to provide and maintain the building space required to house large conventional reformers.
It is therefore an object of the present invention to provide a compact catalytic hydrocarbon reformer which operates at lower temperatures because of an enhanced heat transfer mechanism between the chamber containing the burner combustion gases and the reactor chamber.
It is also an object of the invention to reduce the overall volume of the catalytic hydrocarbon reformer assembly.
A further object of the invention is to provide a catalytic hydrocarbon reformer that minimizes the use of costly, high temperature materials for the components of the reformer.
Another object of the invention is to provide a catalytic hydrocarbon reformer with a lower differential pressure between the burner combustion gases and the process fuel reaction gases, thereby obviating the need to accommodate high internal pressure differentials.
A still further object of the invention is to provide a catalytic hydrocarbon reformer with reduced thermal gradients across the reformer components, thereby increasing the life expectancy of the reforming catalyst and internal components.